v0.2.1

Whats New:

1. fix #2 dispatch_queue usage on ios
2. remove all try/catch statements in native code.
3. add dispatchQueue on android to prevent UI-Thread from getting blocked.
4. Add method to get all keys stored in the database
5. Add an option non-async methods api based on callbacks.
6. Huge performance boost

breaking changes All async method names have changed.